From French Pat. Nos. 2,289,414 and 2,327,172 it is known to apply snow to skiing sites by drawing off snow from a pile and conveying it pneumatically towards the site of use by means of a duct. The equipment described in these patents comprises a fan feeding air into a conveying duct in which a snow injector is provided. The plant associated with the conveying duct may be stationary, the snow drawoff device, the injector and the air generator being permanently placed at their site of use. The plant may also be movable and may comprise the same devices mounted on a vehicle. The snow drawoff device described always moves in a pile of snow or a layer of snow which is stationary. This is either a screw cutting off piled snow in conical slices of various apex angles, one end being integrally secured to an articulated attachment point, the other end describing circles of increasing radius, or a screw mounted on a movable trolley cutting off piled snow in successive transverse slices, or a drawoff device capable of travelling over snow by being mounted on a vehicle.
In document FR-A-2,327,172, the drawoff device placed at the head of the stationary plant conduit refers to that described in the claims of patent FR-A-2,289,414, as described above. Thus, these patents describe a system for drawing off snow wherein the pile of snow or the layer of snow is stationary, and the drawoff device must move, this also being the case in the plant referred to as stationary.
The same applies to French Pat. No. 2,422,771, where the drawoff device, consisting of a cutter or turbo-cutter, moves on an arm which can be directed.
This is also the case in European Patent Application No. 106,731, where only the air generator can form a stationary unit, the drawoff device being always associated with the vehicle for cutting off the pile or the layer of snow, which remains stationary.
The drawoff device consisting of screws such as those described in patent FR-A-2,289,414, does not make it possible to provide sealing between the internal space of the duct and the atmosphere, where the air pressures are different. This results in a mediocre pneumatic efficiency due to the leakages of air from the inside of the duct outwards. The construction involves fairly complex machinery. It is known, furthermore, that snow is a material which rapidly gives rise to a cramming phenomena, and hence to blocking, in the conveying screws.
The drawoff device consisting of a snow cutter or of a turbo-cutter with a single or double drum is efficient, but it has always been considered for use while it travels over the pile or the layer of snow by virtue of a vehicle. This arrangement requires a tracked vehicle capable of travelling over snow, which is high in cost and which is made very difficult to drive by the need to cut the snow off in a uniform manner.
Since this result is very difficult to achieve, it leads to a very nonuniform flow of snow in the duct. This is reflected in a risk of cramming and an actual mean rate of conveying which is much lower than the theoretical maximum output of the plant. This relatively low conveying rate is also due to the losses of time due to the maneuvering of the vehicle.
The use of a wheeled vehicle for moving the drawoff device in the operations of snow removal by pneumatic conveying involves the same disadvantages as those described above.